The present application relates to an electrode having a film on an electrode active material layer and a battery provided with a positive electrode thereof.
In recent years, portable electronic appliances such as a camera-integrated VTR (video tape recorder), a mobile phone and a laptop personal computer have widely diffused, and it is strongly demanded to reduce their size and weight and to achieve their long life. Following this, batteries, in particular, light-weight secondary batteries capable of providing a high energy density have been developed as a power source.
Above all, a secondary battery utilizing intercalation and deintercalation of lithium (Li) for a charge and discharge reaction (so-called “lithium ion secondary battery”) is greatly expected because it is able to provide a higher energy density than a lead battery or a nickel-cadmium battery. Such a lithium ion secondary battery is provided with an electrolytic solution as well as a positive electrode and a negative electrode, and the negative electrode has a negative electrode active material layer on a negative electrode collector.
A carbon material such as graphite is widely used as a negative electrode active material to be contained in the negative electrode active material layer. Also, in recent years, following the development of a high performance and a multi-function of portable electronic appliances, a more enhancement of the battery capacity is demanded. Thus, it is investigated to use silicon, tin or the like instead of the carbon material. This is because a theoretical capacity of silicon (4,199 mAh/g) and a theoretical capacity of tin (994 mAh/g) are significantly higher than a theoretical capacity of graphite (372 mAh/g), and therefore, a large enhancement of the battery capacity can be expected.
However, in the lithium ion secondary battery, the negative electrode active material having lithium intercalated therein becomes highly active at the time of charge and discharge, and therefore, not only the electrolytic solution is easily decomposed, but lithium is easily deactivated. Thus, a sufficient cycle characteristic is hardly obtained. In the case of using, as a negative electrode active material, silicon with a high theoretical capacity or the like, this problem becomes conspicuous. There is also involved a problem that when the cycle proceeds, a decomposition product of the electrolytic solution is deposited on the electrode, whereby the resistance increases.
Then, in order to solve various problems of the lithium ion secondary battery, there have been made a number of investigations. Specifically, in order to enhance a negative electrode characteristic and a low-temperature characteristic, there is proposed a technology for incorporating a phenylsulfonic acid metal salt into an electrolytic solution (see, for example, JP-A-2002-056891). Also, there is proposed a technology for incorporating an organic alkali metal salt into an electrolytic solution (see, for example, JP-A-2000-268863). Furthermore, in order to enhance a storage characteristic and a cycle characteristic, there is proposed a technology for incorporating a hydroxycarboxylic acid into an electrolytic solution (see, for example, JP-A-2003-092137). In addition to this, in order to suppress a lowering of the battery capacity, there is proposed a technology for coating a carbon material which is a negative electrode active material with a lithium alkoxide compound (see, for example, JP-A-08-138745). Also, in order to increase adhesion of an electrode, there is proposed a technology for adding a mercapto group or a sulfide (see, for example, JP-A-09-82311 and JP-A-09-82330).